There is an "alt code" that seems to work (at least for me).
While typing a message in the chat window, press and hold the <alt> key on your keyboard, then key the following numbers on your numeric keypad on the right hand side of your keyboard.... 0-1-1-8-8. Then release the <alt> key.
It'll give you a ¤ in any other editor. But in chat, it'll give you the credit symbol.
Hope that helps.
Edit: Bahh. You were asking about the Cartel Coin symbol, not the credit symbol. My bad. Seems Amber gave you the "actual" answer. Scroll down 1 message.
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